Imide additives for sulfur vulcanizable polymers

ABSTRACT

IMIDES SUCH AS N-(MORPHOLINOTHIO)PHTHALIMIDE ARE USED TO EFFECT THE VULCANIZATION CHARACTERISTICS OF SULFUR VULCANIZABLE POLYMERS BY INCREASING THE STATE OF VULCANIZATION AND/OR IMPROVING SCORCH RESISTANCE AND/OR CREASING THE RATE OF VULCANIZATION.

United States Patent 3,838,114 IMIDE ADDITIVES FOR SULFUR VULCANIZABLEPOLYMERS John P. Lawrence, Stow, Ohio, assignor to The Goodyear Tire &Rubber Company, Akron, Ohio No Drawing. Filed June 26, 1972, Ser. No.266,008 Int. Cl. C08f 27/06; C08c 11/60; C08d 9/00 U.S. Cl. 26079.5 A 8Claims ABSTRACT on THE DISCLOSURE Imides such asN-(morpholinothio)phthalimide are used to affect the vulcanizationcharacteristics of sulfur vulcanizable polymers by increasing the stateof vulcanization and/or improving scorch resistance and/or increasingthe rate of vulcanization.

This invention relates to compounds which generally function to increasethe state (degree) of vulcanization when used during the sulfurvulcanization of rubbers by donating sulfur to the system. Thisinvention also relates to compounds which provide a vulcanizable polymerwith balanced processing and vulcanization characteristics. In addition,it relates to compounds which retard vulcanization during the processingof vulcanizable rubber compositions. It also relates to compounds whichfunction as activators, that is, secondary accelerators in sulfur typevulcanization systems. It also relates to processes for increasing thestate of vulcanization of sulfur vulcanizable rubbery compositions andeither increasing scorch delay periods and/or increasing vulcanizationrates. It also relates to the vulcanized products resulting therefrom.

The physical properties of a vulcanized composition are related to itsstate of vulcanization. Often, as the state of vulcanization isincreased, certain physical properties are improved. Rubber additivessuch as sulfur donors can be used therefore to increase the state ofvulcanization or to permit the use of lesser amounts of free sulfur.

Scorching during the processing of rubber is due to the premature orinsipient vulcanization which can occur during any of the steps involvedin the processing of the rubber prior to the final vulcanization step orduring storage between said processing steps. Whereas a properlycompounded unscorched rubber formulation can be die extruded or sheetedsmoothly from a calender without lumping, a scorched material oftenbecomes Wavy or lumpy after sheeting and must be discarded. It istherefore desirable that rubber additives be used which reducescorching. Such compounds are commonly referred to as retarders.

It is often desirable to increase the rate at which rubbery compositionsare vulcanized. Sulfur vulcanizable rubbery compositions containing freesulfur are made to vulcanize more rapidly by the addition of anaccelerator compound. Ofter the accelerator compound is referred to as aprimary accelerator and is used in combination with another acceleratorcalled an activator or secondary accelerator which further increases thevulcanization rate.

It is an object of this invention to provide sulfur donors which willincrease the state of vulcanization of vulcanized rubbery polymers aswell as compounds which are secondary accelerators (activators) and/ orretarders (scorch inhibitors). Another object of the present inventionis to provide processes which will improve the scorch resistance andrate of vulcanization of vulcanizable rubbery polymers and also thestate of vulcanization of sulfur vulcanized rubbers.

The objects of the present invention are accomplished by a sulfurvulcanizable combination of a sulfur vulcanice izable rubber and atleast one compound having the following structural formulae and CXC

wherein R is a saturated or olefinic divalent aliphatic radical having 1to 7 carbon atoms, such as an alkylene radical or alkenylene radical ora saturated or olefinic divalent cyclic aliphatic radical such as acycloalkylene, cycloalkenylene, or arylene radical and wherein R and Rare selected from the group consisting of alkyl radicals having 1 to 20carbon atoms, cyano alkyl radicals having 2 to 21 carbon atoms,cycloalkyl radicals having 5 to 20 carbon atoms, aralkyl radicals having7 to 20 carbon atoms and aryl radicals (e.g., phenyl, p-tolyl,alkoxyaryl, haloaryl and nitroaryl) having 6 to 20 carbon atoms, whereinR and R can be joined through a member of the group consisting of -CH O,and S- to constitute with the attached nitrogen atom a heterocyclicring, and wherein X is selected from the group consisting of alkyleneradicals having 2 to 10 carbon atoms, cycloalkylene radicals having 5 to10 carbon atoms and arylene radicals having 6 to 10 carbon atoms.

Preferably R is 4,5-cyclohexeny1ene, orthophenylene, ethylene, or1,3-propylene. Preferably is morpholino, 2,6-dimethylmorpholino,piperidino, diethylamino, diisopropylamino, 3-methylpiperidino,t-butylamino, dicyclohexylamino, N [3 cyanoethylcyclohexylamino,N-B-cyanoethyl-t-butylamino, B-cyanoethyl-n-butylamino,N-phenylcyclohexylamino, N-methylanilino, N- ethylanilino,N-ethylbenzylamino, dibenzylamino, N-phenylbenzylamino,N-cyanomethylcyclohexylamino, and cyanomethyl-n-butylamino.

Preferably when A is an N,N'-disubstituted radical which is a derivativeof a heterocyclic diamine, the diamine is piperazine, imidazolidine,hexahydropyrimidine, or homopiperazine, said amines (radicals) beingunsubstituted on the ring carbons by methyl groups, the total number ofmethyl groups being less than three. It should be understood that theabove radicals need not actually be derived from the above diamines butneed only be the radicals which can be derived from said diamines. Thatis, the compounds are not limited to their method of preparation.

More preferably A is piperazine, 2,5-dimethylpiperazine, imidazolidine,hexahydropyrimidine, homopiperazine, N,N-dimethylethylenediamine,N,N-dimethyl-1,3-propylenediamine, N,N'-dimethyl 1,6hexamethylenediamine, N,N-dimethyl-1,4-cyclohexylenediamine,N,N-dimethylp-phenylenediamine, 4,4'-ethylenedi(piperidine),4,4-trimethylenedi(piperidine), 4,4 tetramethylenedi(piperidine) or4,4'-hexamethylenedi(piperidine).

Compounds which act both as retarders and activators in SBR includecompounds where R is orthophenylene or 1,2-cyclohex-4-enylene and ismorpholino, N-phenylcyclohexylamino, N-fi-cyanoethylcyclohexylamino, N13 cyanoethyl n butylamino, N- ethylbenzylamino or Ncyanomethylcyclohexylamino. Where R is one of the two radicals describedabove and is N-phenylbenzylamino the compounds are retarders.

The following compounds illustrate, but do not limlt, the imides of thepresent invention.

N-morpholinothio -phthalimide N- (2,6-dimethylmorpholinothio-phthalimide N- (piperidinothio -phthalimide N- (3-methylpiperidinothio-phthalimide N- (4-methylpiperidinothio -phthalimide N- (pyrrolidinothio-phth alimide N-(diethylaminothio) -phthalimide N-(di-n-propylaminothio) phthalimide N- (diisopropylaminothio)-phthalimide N- (di-n-butylaminothio -phthalimide N-(diisobutylaminothio-phthalimide N- (di-n-hexylaminothio -phthalimide N-(di-n-octylaminothio -phthalimide N- (dicyclohexylaminothio -phthalimideN- (N'-methylcyclohexylaminothio -phth alimide N- (dibenzylaminothio)-phth alimide N-(morpholinothio -cisA -tetrahydrophthalirnideN-(morpholinothio -succinimide N- (piperidinothio -succinimide N-morpholinothio) -maleimide N- (dibenzylaminothio -maleimide N-(morpholinothio -glutarimide N- (2,6-dimethylmorpholino thio)-glutarimide N-(morpholinothio)-1, 8-naphthalimideN-(N'-methylcyclohexylaminothio)-1,8-naphthalimide N- (morpholinothio-hexahydrophthalimide N- (di-rz-propylaminothio -hex ahydrophthalimideN- (morpholinothio -adipimide N-(4-methylpiperidinothio -adipimide N-morpholinothio ,5 -dimethylglutarimide N- (3-methylpiperidinothio)-5,5-dimethylglutarimide N- (morpholinothio 2.2. 1-bicyclohept-4-ene-2,3-

dicarboximide N-(morpholinothio -malonimide N-(N'-phenylcyclohexylaminothio -phth alimide N-(N-fl-cyanoethylcyclohexylaminothio -phthalimide N- N'-,B-cyanoethyl-n-butylaminothio -phthalimide N- (N-ethylb enzylaminothio-phthalimide N- (N-phenylbenzylaminothio -phthalimide N-(N'-cyanomethylcyclohexylarninothio -phthalimide N,Ndimethyl-N,N-bis(phthalimidothio) -ethylenediamineN,N'-dimethyl-N,N'-bis(phthalimidothio) -1,3-propylenediamineN,N-dimethy1-N,N-bis (phthalimidothio)-1,6-hexamethylenediamineN,N-dimethyl-N,N-bis (phthalimidothio) -1,4-cycl0- hexanediamineN,N'-dimethyl-N,N'-bis (phthalimidothio -p-phenylenediamine 1,4-bis(phthalimidothio -piperazine 1,4-bis (phthalimidothio -homopiperazine1,4-bis (phthalimidothio -2,5-dimethylpiperazinc 1,3-bis(phthalimidothio -imidazolidine 1,3 -bis (phthalimidothio-hexahydropyrimidine 4,4'-ethylenedi (piperidinothio -bis- (phthalimide)4,4'-tetramethylenedi (piperidinothio -bis (phthalimide)4,4'-hexamethylenedi (piperidinothio -bis (phthalimide) When used with aconventional primary accelerator and sulfur, the compounds of structuralformula (I) provide a vulcanizable polymer with balanced processing andvulcanization characteristics. In many vulcanization systems theyprovide both improved scorch resistance and improved activationcharacteristics. In systems where they provide only improved scorchresistance or improved activation characteristics, they do so withoutadversely affecting the scorch resistance or conversely the activationcharacteristics. This is unique in that conventional retarders normallyadversely affect vulcanization rates, much less improve the rate; whileconventional activators normally adversely affect scorch, much lessimprove scorch resistance. Whether these compounds act as bothactivators and retarders, or just as an activator, or just as aretarder, is not only dependent upon the primary accelerator being usedbut also upon the particular polymer being vulcanized as well as theparticular sulfur donor compound of the present invention being used.The effect of accelerator systems, polymeric environment and differentsulfur donor compounds is illustrated herein. It should be noted,however, that regardless of the accelerator system used or theparticular polymer vulcanized, the compounds almost always act as sulfurdonors. In any case, the imides of the present invention will act atleast as one of the following; a sulfur donor, an activator or aretarder.

The imides of the present invention can be prepared by the reaction ofan aminesulfenyl chloride with an alkali metal salt of an imide.Alternately, the aminesulfenyl chloride may be reacted with an imide inthe presence of an organic acid acceptor such as pyridine ortriethylamine. The aminesulfenyl chlorides, in turn, may be preparedusing any of the available methods described in the literature, forexample, by chlorination of N,N'-dithiobis(amine) [German Pat. 965,968(1954)], or by the reaction of a secondary amine with sulfur dichloridein the presence of an organic acid acceptor [German Pat. 1,131,222(1962)]. Generally a solution of the aminesulfenyl chloride in an inertsolvent is added to a solution or suspension of the imide (or its alkalimetal salt), also in an inert solvent.

Alternatively, the imides can be prepared by reaction of animide-N-sulfenyl chloride with an appropriate amine in the presence ofan organic acid acceptor such as triethylamine or pyridine, or an excessof the amine which is entering into the reaction with theimide-N-sulfenyl chloride. The imide-N-sulfenyl chlorides, in turn, arereadily prepared as described in the literature by reaction of an imidewith sulfur dichloride in the presence of an organic acid acceptor [U.S.Pat. 3,539,538 (1970)]. Generally, an amine is added to a solution ofthe imide- N-sulfenyl chloride in an inert solvent.

The preformance of the compounds of the present invention as retarders,activators or in increasing the state of vulcanization is not dependentupon their method of preparation.

The imides of the present invention can be used with any conventionalcompounding additive such as carbon black, zinc oxide, antidegradantsand stearic acid. They can be used in a sulfurless system with anaccelerator (a sulfur donor or otherwise), preferably a primaryaccelerator, or with a sulfur vulcanization agent in the presence of anaccelerator. For the purposes of this invention, sulfur vulcanizingagent means elemental sulfur (free sulfur) or sulfur donatingvulcanizing agents, for example, an amine disulfide or a polymericpolysulfide. Preferably the imides are used with both a sulfurvulcanization agent, preferably free sulfur, and an accelerator,preferably a primary accelerator. The invention is applicable tovulcanization accelerators of various classes using conventionalaccelerator levels. Regardless of what accelerator is used, the imideswill still normally act as sulfur donors. For example, rubber mixescontaining the aromatic thiazole accelerators which includesN-cyclohexyl-2 benzothiazolesulfenamide, Z-mercaptobenzothiazole,N-tert-butyl-2-benzothiazolesulfenamide, 2-benzothiazolyldiethyldithiocarbamate and 2-(morpholinothio)- benzothiazole can beused. Other thiazole accelerators which may be used include2-(aminodithio)-thiazoles and 2-(aminotrithio)-thiazoles such asZ-(morpholinodithio)-benzothiazole. Amine salts of mercaptobenzothiazoleaccelerators, for example, the t-butylamine salt ofmercaptobenzothiazole, and like salts of morpholine and2,6-dimethylmorpholine can be used in the invention. Thiazoleaccelerators other than aromatic can be used. Stocks containingaccelerators, for example, tetramethylthiuram disulfide,tetramethylthiuram monosulfide, aldehyde amine condensation products,thiocarbamylsulfenamides, thioureas, xanthates, and guanidinederivatives are substantially improved using the process of the presentinvention.

The imides of the invention can be used in any sulfur vulcanizablerubber including natural and synthetic rubbers andmixtures thereof.Synthetic rubbers that can be improved by the process of this inventioninclude homopolymers and copolymers of dienes, both conjugated andnonconjugated, e.g., 1,3-dienes such as 1,3-butadiene and isoprene.Examples of such synthetic rubbers include neoprene (polychloroprene),cis-1,4 polybutadiene, cis- 1,4 polyisoprene, butyl rubber, copolymers,of 1,3-butadiene or isoprene with monomers such as styrene,acrylonitrile and methyl methacrylate. Ethylene/propylene terpolymers,for example ethylene/propylene/dicyclopentadiene terpolymers alsobenefit from the practice of the present invention.

The imides can be added to the rubbers by any conventional techniquesuch as milling or Banburying.

All of the working examples herein are intended to illustrate but notlimit the scope of the present invention. Unless indicated otherwise,all parts are parts by Weight.

The following examples, 1 to 7, illustrate the preparation of variousimides of the present invention, and are not intended to limit the scopeof the present invention.

EXAMPLE 1 To prepare N-(morphorinothio)-phthalimide, 0.50 mole ofchlorine gas was added during one-half hour to a mixture of 118.0 gramsof 4,4-dithiobis(morpholine) in 500 ml. of toluene at 5 C. The resultingsolution of morpholinesulfenyl chloride was added during one hour to amixture of 147 grams (1.0 mole) phthalimide, 120 grams (1.2 mole)triethylamine, and one liter tetrahydrofuran at 50 C. After one hour,the mixture was poured into 1.5 liters of water, the insoluble solidfiltered, washed on the filter with water, and recrystallized from2-propanolbenzene to afford 161.3 grams (61.0%) of the product having amelting point of 210- 212 C. Analysis of the product showed 10.55percent nitrogen and 12.13 percent sulfur. The percentages calculatedfor C H N O 'S were 10.68 percent nitrogen and 12.12 percent sulfur.

6 EXAMPLE 2 To prepare N-(diethylaminothio)-phthalimide, 0.20 mole ofchlorine gas was added during 15 minutes to a solution of 41.5 grams(0.20 mole) -N,N-dithiobis(diethylamine) in ml. of carbon tetrachlorideat 0-5 C. The resulting solution of diethylaminesulfenyl chloride wasadded dropwise to a mixture of 58.7 grams (0.40 mole) phthalimide, 48.5grams (0.48 mole) triethylamine, and 250 ml. of tetrahydrofuran at 010C. After onehalf hour, the mixture was poured into three liters ofwater, extracted with chloroform, the combined extracts dried overanhydrous magnesium sulfate, and concentrated in vacuo. The resultingsolid residue was recrystallized twice from methanol, then stirred forten minutes in 350 ml. of ice cold one percent sodium hydroxide,filtered, washed on the filter with water and dried in vacuo. The yieldof product was 36.7 grams (36.7%) with a melting point of 73-75 C.Analysis showed 11.06 percent nitrogen and 12.9 percent sulfur. Thepercentages calculated for C H N O S were 11.20 percent nitrogen and12.8 percent sulfur.

EXAMPLE 3 To prepare N-(piperidinothio)-phthalimide, 0.20 mole ofchlorine gas was added to a solution of 46.4 grams (0.20 mole)N,N-dithiobis(piperidine) in 100 ml. of carbon tetrachloride during 15minutes at 0-5 C. The resulting solution of piperidinesulfenyl chloridewas added dropwise during twenty minutes to a mixture of 58.7 grams(0.40 mole) phthalimide, 48.5 grams (0.48 mole) triethylamine, and 450ml. of tetrahydrofuran at 0-l0 C. After one hour, the mixture was pouredinto 2.5 liters of water, sufficient chloroform added to dissolve theinsoluble solid, the lower layer drawn off, dried over anhydrousmagnesium sulfate, and concentrated in vacuo. The resulting solidresidue was recrystallized twice from 2-propanol-benzene, then stirredfor ten minutes in 550 ml. of ice cold 0.5 percent sodium hydroxide,filtered, washed on the filter with water and dried in vacuo. The yieldof product was 62.5 grams (59.6%) with a melting point of 177l79 C.Analysis showed 10.57 percent nitrogen and 10.8 percent sulfur. Thepercentages calculated for C13H14N2O2S were 10.69 percent nitrogen and12.2 percent sulfur.

EXAMPLE 4 To prepare N-(diisopropylaminothio)-phthalirnide, 0.25 mole ofchlorine gas was added to a solution of 67.1 grams (0.25 mole)N,N'-dithiobis(diisopropylamine) in 100 ml. of carbon tetrachlorideduring fiteen minutes at 05 C. The resulting solution ofdiisopropylaminesulfenyl chloride was added dropwise during one-halfhour to a stirred mixture of 74.5 grams (0.50 mole) phthalimide, 61.6grams (0.62 mole) triethylamine and 250 ml. of tetrahydrofuran at 010 C.After one hour the mixture was poured into three liters of water,extracted with chloroform, the combined extracts dried over anhydrousmagnesium sulfate, and concentrated in vacuo. The oily solid residue wasslurried in hexane, filtered, then stirred in 650 ml. of ice cold 0.5percent sodium hydroxide for ten minutes, refiltered, washed with water,and recrystallized twice from methanol. The yield of product was 64.5grams (45.6%) with a melting point of 98100 C. Analysis showed 9.94percent nitrogen and 11.4 percent sulfur. The percentages calculated forC H N O S were 10.7 percent nitrogen and 11.5 percent sulfur.

EXAMPLE 5 To prepare N (morpholinothio) cis A tetrahydrophthalimide,0.10 mole of cholrine gas was added to a solution of 23.6 grams (0.10mole) 4,4'-dithiobis(morpholine) in 100 ml. of ethylene dichlorideduring ten minutes at 0-5 C. The resulting solution ofmorpholinesulfenyl chloride was added dropwise to a mixture of 30.2grams (0.20 mole) cis-A -tetrahydrophthalimide, 24.2 grams (0.24 mole)triethylamine, and 250 ml. of ethylene dichloride. After one hour thereaction mixture was filtered, the filtrate concentrated in vacuo, thesolid residue slurried in heptane, refiltered, and recrystallized from2-propanolbenzene. The product was further purified by stirring forone-half hour in 200 ml. of 25 percent potassium carbonate, filtering,Washing with water, and drying in vacuo. The yield of product was 27.0grams. (50.5%) with a melting point of 142145 C. Analysis showed 10.47percent nitrogen and 11.83 percent sulfur. The percentages calculatedfor C H N O S were 10.45 percent nitrogen and 11.94 percent sulfur.

The other compounds included within the practice of the presentinvention can be prepared by using the same or similar techniques asdescribed in the preceding working examples. Synthetic routes to thesecompounds are not limited, however, to these particular reactions andprocedures.

Tables I, II, III and IV illustrate the use of various imides of thepresent invention with different rubber stocks. The compositions areintended only to be illustrative of the practice of the presentinvention and not limiting. Mooney Scorch tests were performed using thelarge rotor as described in ASTM D 1646-61. A recorder was employed tocontinuously plot viscosity versus time. The number of minutes (2A5)required for the viscosity curve to rise five points above the minimumwas taken as a measure of scorch inhibition. Larger values for (1A5)indicate a greater resistance to scorch or premature vulcanization.

Data on vulcanizing characteristics were obtained with a MonsantoOscillating Disc Rheometer, as described by Deck, Wise, and Guerry inRubber World, page 68, December 1962. Pertinent data from thisinstrument are: t.;, the minutes required for the Rheometer torque curveto rise four units above the minimum torque value, and 1 the minutesrequired for the torque curve to reach 90 percent of the differencebetween the maximum and minimum torque values.

The r,,,, value is considered to be the time required to reach theoptimum vulcanized state. The difference, U -t is indicative of the timenecessary for actual vulcanization to take place after the scorch delayperiod has ended, i.e., is a relative measure of vulcanization rate.Compounds which increase 1 but do not greatly increase (r -t arepreferred since these impart processing safety, yet do not requiregreatly extended vulcanization times.

ARh is the difference between the maximum and minimum torque obtained onthe rheometer curve. It is used as a measure of the degree (state) ofvulcanization.

The following Examples 6 to 26 illustrate the use of the sulfur donorsof the present invention in both natural rubber and SBR(butadiene/styrene elastomer). Stock A was used in Examples 6 to whileStock B was used in Examples 16 to 26. Both stocks were run with noimide (control), 0.5 part and 1.0 part of the imide.

8 natural rubber and 302 F. in SBR. The Mooney Scorch data wasdetermined at 250 F. in natural rubber and 270 F. in SBR.

The effect of the imides was measured by comparison with the control,i.e., the stock with no imide present. Ratios of the measurements forthe imide compounded stocks over the measurements for the control stockare listed in the tables. The c subscript indicates that the measurementwas made on the control stock. Values of ARh/AR/z which are over 1.00indicate that the imide has increased the state of vulcanization. Valuesof (t =t )/(t t which are less than 1.0, indicate an activating effectof the imide on the vulcanization rate. Values of tA /tA which are over1.0 indicate that the imide has increased the scorch delay time, i.e.,increased scorch resistance.

Table II contains a list of the various imides evaluated,

TABLE II Imide:

(A) N-(morpholinothio)-phthalimide (B N-diethylaminothio -phth alimide(C) N-(piperidinothio)-phthalimide (D)N-(diisopropylaminothio)-phthalimide (E) N-(morpholinothio)-cis-A-tetrahydrophthalimide (F) N- (N-phenycyclohexylaminothio -phthalimide(G) N-(N-B-cyanoethylcyclohexylaminothio)- phthalimide (H)N-(N'-a-cyanoethyl-n-butylaminothio)- phthalimide (I)N-(N-ethylbenzylaminothio)-phthalimide (IN-(N-phenylbenzylaminothio)-phthalimide (K)N-(N-cyanomethylcyclohexylaminothio)- phthalimide TABLE TIL-NATURALRUBBER (too-l4) ARh/ARh 1.0-t1): ins/m5,

(P (P (pa s) Exp Imide 0.5 1.0 0.5 1.0 0.5 1.0

1. 14 1. 20 1. 00 1. 00 1. 1. 75 1. 20 1. 31 0.85 0. 02 1. 24 1. 45 1.13 1.10 0. 01 0. 84 0.00 0.87 1.14 1. 2a 0.85 0. s7 1. 32 1.45 1. 031.04 1.05 1.15 1.10 1.41 1. 05 1. 13 0. 03 0. 07 1. 27 1. 1. 11 1. 150.87 0. 0a 1. 42 1. 55 1. 15 1. 21 0.85 0. 88 1. 35 1. 50 1. 02 1.08 0.00 1. 04 1. 27 1. 47 1.12 1.10 1.02 1.04 1.27 1.47

TABLE IV.SBR

(loo- 4) ARh/ARhu (two-00 c (p (p (p 1. 00 1. 20 0. 7s 0. 74 1. 20 1. 451.14 1.24 0. 05 0. 53 0.02 0.07 1. 00 1.15 0.63 0.51 0.00 0.00 1. 10 1.15 0. 75 0. 02 0. 00 0. as 1. 05 1. 1a 0.87 0. 76 1. 05 1. 1s 0. 00 0.0s 0. 04 0. 00 1. 12 1. 22 1.03 1.04 0.00 0.78 1 10 1.27 1.01 1.05 0.830. 73 1 20 1. 2s 0. 08 1.07 0.70 0.63 1.12 1.22 1. 02 1. 03 1. 020.98 1. 05 1. 10 1. 06 1. 11 0. 03 0. 05 1. 00 1. 17

TABLE I Sto-k A Stock B parts) (parts) SB R 1712 137. 5 Smoked sheets.Carbon black Stearic Wax- Zinc oxide Ammo antioxidant Sulfur 2.5 1.52-(morpho 0. 5 1 Imide 0-0. 5-1. 0 0-0. 5-1. 0

N-(morpholinothio)-phthalimide was used in carbon black loaded naturalrubber (smoked sheet) with 2.5 parts of sulfur at both the 0.5 and 1.0part level, with 2- (morpholinodithio)-benzothiazole (0.5 part) in oneinstance and 0.5 part of 2-(2,6-dimethylmorpholinothio)- bcnzothiazolein another. In the former case, the imide acted as a sulfur donor andretarder. In the latter instance, it acted as a sulfur donor, activatorand retarder. The imide was also used with 0.5 part of three otheraccelerators separately. When used with 2-(morpholinothio) benzothiazoleand N-cyclohexyl-Z-benzothiazolesulfenamide, in both instances it actedas a sulfur donor, 2. retarder and an activator. When used withN-t-butyl-2 benzothiazolesulfenamide, it acted as a sulfur donor and aretarder, while having only a small adverse effect on the vulcanizationrate.

N-(morpholinothio)-phthalimide was used in various other carbon blackloaded stocks containing free sulfur. In an NBR(butadiene/acrylonitrile) stock and a cis-1,4- polyisoprene stock, itwas used with a primary/secondary accelerator system and sulfur. In bothcases the state of vulcanization and scorch delay period were increased.In a natural rubber/SBR cis-1,4 polybutadiene blend it was used with aprimary accelerator and sulfur and increased the state and rate ofvulcanization and the scorch delay time. It was also used in a naturalrubber composition containing sulfur and a primary accelerator usingvarious activators (secondary accelerators). It provided an increasedrate and state of vulcanization. It was also used with free sulfur and aprimary accelerator in a natural rubber/SBR blend and in a cis-1,4polybutadiene composition. In both cases the rate and state ofvulcanization were increased along with the scorch delay period. It wasalso used in natural rubber with both sulfur and a primary acceleratorusing diphenylguanidine in one case as a secondary accelerator andtetramethylthiuram disulfiide in another instance. In both cases ahigher state of vulcanization and increased scorch delay time wereobtained.

The imide (0.5 part) was also used in a carbon black loaded smoked sheetcomposition, in one instance with benzothiazyl disulfide (0.5 part), andin another instance with 0.5 part of Z-mercaptobenzothiazole. In bothinstances the imide increased the rate and state of vulcanization andacted as a retarder.

The imide was also used in a smoked sheet natural rubber composition atboth the 0.5 and 1.0 part levels, in one instance with 1.0 part of2-(morpholinothio)-benzothiazole and in another instance with 1.0 partof 2- mercaptobenzothiazole. In every instance the imide acted toincrease the state of vulcanization. Also, in every instance itincreased the rate of vulcanization with one exception (the sulfenamideat the 1.0 part level). With the sulfenamide it also acted as aretarder. It was also used at the 0.5 and 1.0 part levels with the2-(morpholinothio)- benzothiazole in combination with sulfur (2.75 part)and tetramethylthiuram disulfide. In both instances it increased thestate of vulcanization and the scorch delay time.

A natural rubber composition was cured without sulfur using 1, 1.5, and2.0 parts of the imide along with, in one instance, 0.5 part of2-(morpholinodithio)-benzothiazole and in another instance with2-(rnorpholinothio)- benzothiazole. In each instance the state ofvulcanization and scorch delay period were increased.

The above examples are not intended to be limiting but ratherillustrative. Any of the sulfur donors, accelerators and rubbersdescribed earlier herein can be substituted in the preceding examples.In addition, the levels of the sulfur donors and other components insaid examples could be altered in accordance with the general teachingsherein.

The additives of this invention can be used at various concentrations aslow as 0.25 part per 100 parts by weight of rubber and even as low as0.10 or even 0.05 part. Con- 10 ventional levels would frequently be 0.5and 1.0 part, although levels as high as 1.5, 3.0, 5.0 and even 10 partscan be used. Most frequently the concentration ranges from 0.25 to 5.0parts, more preferably from 0.25 to 3.0 parts and most preferably from0.25 to 1.50 parts.

The sulfur donor compounds of the present invention are preferably addedto the rubbery polymer at the same time that the accelerator is added,although this order of addition is not necessary to the successfulutilization of the compounds of this invention.

The compounds of the present invention are effective in the presence oforganic accelerators whether they are diarylguanidines such asdiphenylguanidine, or thiazoles, more specifically benzothiazyl aminodisulfides, such as 2 (morpholinodithio)-benzothiazole, or thiazoles(also sulfenamides), more specifically thiazolesulfenamides, and evenmore specifically benzothiazolesulfenamides such as2-(morpholinothio)-benzothiazole andN-cyclohexyl-Z-benzothiazolesulfenamide, i.e., regardless of what typeof organic accelerator is used. Thiuram sulfides such astetramethylthiuram' monosulfide and disulfide and tetraethylthiurammonosulfide and disulfide may also be used as well as otherbenzothiazolesulfenamides such as N- t-butyl-Z-benzothiazolesulfenamide.

Various organic accelerators useful within the practice of thisinvention are described and illustrated in the Vanderbilt RubberHandbook, 1968 Edition, R. T. Vanderbilt Company, Inc., particularly atpages 242 and 244 and also in the bulletin of the Elastomer ChemicalsDept. of the E. I. du Pont de Nemours and Co. (inc.) entitled,Accelerators, Vulcanizing Agents and Retarders, Brochure No. SD AS4457.

The polymers in which the imides of the present invention areincorporated remain suitable for their art recognized uses, e.g., intires and industrial products.

Compounds referred to earlier herein as being retarders and/ oractivators in natural rubber and SBR are merely illustrative and notlimiting.

The balanced processing and vulcanization characteristics are most oftenobtained when free sulfur (elemental sulfur) and a primary acceleratorare used with the imide.

Sometimes compounds are both a sulfur donor (and therefore a sulfurvulcanizing agent) and an accelerator, e.g., 2(morpholinodithio)-benzothiazole. Such compounds can be used with theimides, with or without another sulfur vulcanizing agent and/ or anotheraccelerator.

The compounds of the present invention can be used effectively in anysulfur vulcanizable polymer and with any organic accelerating agent.

In addition to other preferred radicals mentioned earlier herein, apreferred form of R is the ethenylene radical.

Preferably when R is a saturated or olefinic divalent cyclic aliphaticradical, it contains 5 to 7 carbon atoms. When R is an arylene radical,preferably it contains 6 to 10 carbon atoms.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

1. A sulfur vulcanizable diene polymer selected from the groupconsisting of natural rubber and synthetic diene polymers prepared froma monomer system containing diene monomer, said sulfur vulcanizablediene polymer having incorporated therein at least one imide having thefollowing structural formula wherein R is selected from the groupconsisting of satu rated or olefinic divalent aliphatic radicals having1 to 7 carbon atoms, saturated or olefinic divalent cyclic aliphaticradicals having 5 to carbon atoms and arylene radicals having 6 to 10carbon atoms and wherein R and R are selected from the group consistingof alkyl radicals having 1 to 20 carbon atoms, cyanoalkyl radicals have2 to 21 carbon atoms, cycloalkyl radicals having 5 to 20 carbon atoms,aralkyl radicals having 7 to 20 carbon atoms and aryl radicals having 6to 20 carbon atoms, and wherein R and R can be joined through a memberof the group consisting of CH O, and S to constitute with the attachednitrogen atom a heterocyclic ring.

2. The sulfur vulcanizable diene polymer according to claim 1 wherein Ris selected from the group consisting of 4,5-cyclohexenylene,orthophenylene, ethylene and 1,3- propylene, and

is selected from the group consisting of morpholino, 2,6-dimethylmorpholino, piperidino, diethylamino, diisopropylamino,3-methylpiperidino, t-butylamino, dicyclohexylamino,N-fl-cyanoethylcyclohexylamino, N-[i-cyanoethylt butylamino,N-[i-cyanoethyl-n-butylamino, N-phenylcyclohexylamino, N methylanilino,N-ethyl-anilino, N- ethylbenzylamino, dibenzylamino,N-phenylbenzylamino, N cyanomethylcyclohexylamino andN-cyanomethyl-nbutylamino.

3. The sulfur vulcanizable diene polymer according to claim 1 whereinthe polymer has incorporated therein an organic accelerating agent.

4. The sulfur vulcanizable diene polymer according to claim 1 whereinthe polymer has incorporated therein a sulfur vulcanizing agent.

5. The sulfur vulcanizable diene polymer according to claim 3 whereinthe organic accelerating agent is a primary accelerator and the polymerhas incorporated therein elemental sulfur.

6. The sulfur vulcanizable diene polymer according to claim 1 whereinthe imide is present in the amount of from 0.25 part to 5.0 parts byweight per parts by weight of polymer.

7. The sulfur vulcanizable diene polymer according to claim 1 whereinthe polymer is selected from the group consisting of natural rubber,polychloroprene, cis 1,4 polybutadiene, cis-1,4 polyisoprene, butylrubber, copolymers of butadiene and styrene, copolymers of butadiene andacrylonitrile and terpolymers of ethylene, propylene anddicyclopentadiene.

8. The sulfur vulcanizable diene polymer according to claim 1 whereinthe imide is selected from the group consisting ofN-(morpholinothio)-phthalimide, N-(piperidinothio) phthalimide andN-(morpholinothio)-cis-A tetrahydrophthalimide.

References Cited UNITED STATES PATENTS 12/1970 Coran 260-795 B 6/1972Schubart 26079.5 B

JOSEPH L. SCHOFER, Primary Examiner C. A. HENDERSON, JR., AssistantExaminer g gg STATES'PATENT armor" CERTIFICATE CTION Patent No. 3, 3Bat-d September 2 197 Inventor) Johll P. Lawrence It in certified thaterror appears in the above-identified patent: and that said LettersPatent are hereby corrected ea shown Below: I

Cola 2, lines '59 and 60 "[3-cyanoethyl-n-butylamino" should readN-B-cyanoethyl-n-butylamino v line 62, "cyanomethyl-n-butylamino" shouldread N- cyanomethyl-n-butylamino Col.; 3, line 32-,"N-morpholinothio)-phthalimide' should read N-,-(morpholinothio)-phthalimide Col. 1-, line 68,"--"rpreformance' should readperformance Col. 5, line 59, F'N-(morphorinothio)-phthalimide" shouldread N-(morpholinothio)-phthalimide C010 6, line 67, "'10s?" should'readlOO7 -Y-;

v line '71, "eholrine' should read chlorine Cole 8, line 12, "(t =tshould read (t -t J line 27, "N-N-phenycyclohexylamino%hio)-phthalimide". should readN-(N'-phenylcyclohexylaminothio)- phthalimide 7 line 30,"N-(N'-a-cyanoethyl-n-butylaminothio)-phthalimide" should readN-(N'-fiacyanoethyl-n-butylaminothio)- phzzhalimigle line 1; -t1 shouldread t -t 83, E1 cp. '7, "0.85" should ead O:8

line last column of Table IV should read as follows:

1A2 97 0.38 Ov '7 1.18 120 127 129 122 118 115 v Signed and sealed this31st day of December ".374.

(SEAL) Attest:

McCOY M. GIBSON JR. (3. MARSHALL DANN attesting Officer Commissioner ofPatents

